Bow bulb for ships



Feb. 2s, 1967 H SCHNEEKLUTH ET A; 3,306,244 k BOW BULB FOR SHIPS Filed Aug. 25, 1965 5 Sheets-Sheet 1 /NI/f/VTORS A rvr.;

H. SCHNEEKLUTH ET AL 3,305,244

Feb. 28, 1967 BOW BULB FOR SHIPS 3 Sheets-Sheet 2 Filed Aug. 25, 1965 N VEN ro/zs T 5 cms/55m ww H ERBE@ Feb. 28, 1967 H. scHNEEKLuTH ETAL 3,306,244

BOW BULB FOR SHIPS Filed Aug. 25, 1965 '3 sheets-sheet :s

/NVENTORS United States Patent Office 3,306,244 Patented Feb.. 28, 1967 3,306,244 BOW BULB FOR SHIPS Herbert Schneekluth, Aachen, and Friedrich Ahrens, Altenholz, Germany, assignors to Paul Lindenau Schitlswerft und Maschinenfabrik, Kiel-Friedrichsort, Germany Filed Ang. 25, 1965, Ser. No. 482,484 4 Claims. (Cl. 114-56) This invention relates to a bow bulb for shi-ps designed to improve a ships seaworthiness especially in head sea.

In ships having only a small local freeboard at the bow, the forecfastle is liable to be Washed by the head sea. Particularly disagreeable are such Iphases in which the diving of the forecast-le -coincides with a wave crest at the bow.

As is known, a dry forecastle in a head sea can be attained by appropriate configuration, such as:

(l) A high local freeboard at the bow;

(2) Heavily sloping forecastle ribs;

(3) A large coeflicient of fneness ofthe displacement and of the water lines.

Making the local freeboard higher means in most cases a larger ship. Providing more heavily sloping ribs often is not eilicient enough as a sole measure and results in an increased sea resistance. Augmenting the coeflicients of fineness of the displacement and of the water lines also involves an increase in resistance which makes itself felt even in a smooth sea and t-o an increased extent in a rough sea. The hitherto known measures thus involve disadvantages.

In a known bow bulb, the rib shape has a curved limitation. Such a bow bulb favourably influences the displacement current. A disadvantage consists in the occurrence of slamming effects in a rough sea. Similar to normal forecastle shapes, the known bow bulb opposes only insignificant hydrodynamic resistance to pitching.

Finally, pitch damping surfaces, similar to the front hydroplanes in a submarine, have become known in ships which, however, will cause very disagreeable slamming effects when they emerge in a heavy sea.

The present invention provides -a bow bulb for ships i comprising lateral limitations forming a breaking edge located in the regi-on of the largest width of said bow bulb.

Due to this feature, the advantageous influence on the displacement current is maintained. Moreover, the following advan-tages not present in the standard bow bulb can be attained thereby:

(l) Damping of the pitch vibrations due to increased hydrodynamic vertical resistance. With the oblique approach ilow produced by the pitching the thread of stream can break away at the edge. The breaking edges iniluence the pitching motion in the same way as a bilge keel influences the rolling motion.

(2) Reduced slamming effects. The underside of the bulb below the breaking edge may be cuneiformly tapered, thereby to obtain reduced slamming effects as compared with a rounded underside.

(3) Further reduction of resistance by baille action. The flanks of the breaking edges exert a kind of baflle action influencing the wave pattern and thus providing a reduction of resistance beyond the rate given by the displacement current.

(4) Additional reduction of resistance due to the position of the bulb close to the water level. As is known, the influence of the bulb lon the wave pattern is most effective if the bulb is positioned close below the water level. With a standard bulb, the advantage of the resistance is not utilized to avoid the slamming effects which may be produced in this position. But since a bow bulb with a breaking edge can be constructed more slammingproof, the advantage of the position close to the water level can be 4utilized in this case.

(5 Cheaper construction. The bow bulb with a bre-aking edge (bead) can be so designed that the underside is constituted for the most part of plates bent in one direction only, whereas the top of the bulb may even be plane.

The breaking edges may be arranged to extend in the direction of the thread of stream with a smooth water surface.

Also, Ian arrangement is possible in which the breaking edges of the bow bulb deviate from the direction of the thread of stream with a smooth water surface, which enables the damping effect to be increased The wave pattern, furthermore, can be so influenced that there will result -a reduced resistance. The orientation of the breaking edges influences the flow direction from the position of the bow lbulb up to the water level so as to obtain a reduced wave formation `and thus a reduced resistance.

In accordance with another feature of the present invention, the breaking edge may be rounded, whereby it is achieved that the current will be broken away only with the occurrence of heavier pitching. Above the breaking edge, the flanks of the bow bulb may be straight, convex or concave, in order to influence the damping action and the reduction of resistance as desired.

The present invention also provides for the subsequent attachment of breaking edges or breaking edge bodies to a known bow bulb or a standard bow. In such case the breaking edge then constitutes a separate part to be attached -to the existing bow in the way adopted with wedgeshaped bilge keels.

Three embodimentsA of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevation of a bow bulb with a breaking edge having arcuate upper and lower flanks;

FIG. 2 is a diagrammatic representation of horizontal longitudinal sections through the bow bul-b of FIG. l;

FIG. 3 is a diagram showing rib cross sections of the bow bulb of FIG. 1

FIG. 4 is a diagram showin-g rib cross sections of a bow bulb with a breaking edge having Ia plane top surface and alower ilank bent in one direction only, and

FIG. 5 is a diagram showing a standard bow bu-lb provided with an attached breaking edge.

With reference now to FIGS. l to 3, a bow bulb 1 has a base 2 and a breaking edge 3. The bow bulb 1 is represented in the region of ribs 19, 19%, 191/2, 19%, 20 and 20%. The exact shape of the bow bulb 1 results from water lines WLli, WL1/2, WLSA, WL1, WL11/2, WLZ, WL21/2 and WL3, The vships centre line is referenced 4.

FIG. 4 illustrates a different embodiment of a bow bulb with a breaking edge The bow bulb referenced 1 is represented in the region of ribs 171/2, 18, 181/2, 19, 191/2 and 19%. The shape of the bulb results from water lines WLMi, WL1/2, WL1, WLZ, WLS, WL4 and WLS.

In FIG. 5, a bow bulb 1" is provided with a breaking edge 3 formedby an attached part 5 adapted to be subsequently mounted on existing ships bows of any shape. Briefly in review, constructions are known in which the configuration at the bow of a ship is such that it forms a hollow and outer edge extending in the longitudinal direction of the ship.

In the known constructions the edge increases the amount of flow resistance in vertical direction when a vertical flow component is lcaused by the orbital motion of a rough sea or by the pitching motion of the ship.

A vertical force occurs which tends to adjust the motion of the bow to the vertical motion of a rough sea. When the ship pitches in a rough sea in such a manner that t-he water flows alongsid-e the edge, then the pitching vibrations are not influenced otherwise than in accordance with the norma-l configuration of the ship. In such a case, a rough seais relatively harmless.

The present invention provides a combination of longitudinal edges which damp the pitching vibrations and a bow bulb which projects beyond the front vertical line. The invention consists in the combination of the following features:

(a) The bow bulb projects lbeyond the front vertical line below the construction water line;

(b) its two lateral faces are bent in such a way that they form on each side of the ship an ed-ge which is positioned in the region of the largest width of the bow bulb;

(c) the edge slopes backwards in the region behind the front vertical line and has an angle of 6 to 18 relative to the horizontal line in the entire region or in a part thereof;

(d) in the region behind the rear vertical line the edge diverges backwards relative to the midships plane, extends parallel or converges slightly backwards but not more than by 10.

This arrangement not only combines the resistance-decreasing effect of a bow bulb projecting beyond the vertical line with the pitching-Vibration damping effect of llongitudinal edges, but it also increases the effectiveness of the edge in comparison with the known arrangements in the following way:

(1) The lever arm between the front edge portion and the center of the pitching vibrations is enlarged.

(2) Insofar as the bulb is not overlapped by the forecastle, it may be provided with a relatively flat upper side which has the effect of a pitching-vibration damping surface.

In accordance with another feature of the present invention, the edge may be rounded, whereby it is achieved that the current will be broken away only with the occurrence of heavier pitching. Above the edge the anks of the bow bulb may be straight, convex or concave in order to influence the damping action and the reduction of resistance as desired.

Below the bulb the flanks in the plane of ythe ribs may be straight or convexly bent.

The present invention also provides for the subsequent attachment of edges or edge bodies to a known bul-b bow which projects rbeyond the front vertical line. In such a case the edge constitutes a separate structural part to be attached to the existing bow in the Way adopted with wedge-shaped bilge keels.

We claim:

1. In a ship hull comprising a vertical edge at the forward portion of the lbow, a base and a normal water line, the improvement comprising a bow-bulb projecting beyond said hull vertical edge and disposed below the normal water line, said bow-bulb including `lateral faces forming a longitudinal edge extending substantially from the forwardmost portion of said bow-bulb and rearwardly and angularly toward the base of said hu-ll, said longitudinal edge being disposed at the maximum transverse width of said 'bow-bulb and extending substantially the entire ylength of said bow bulb.

2. In a hull for a ship comprising in combination: a hull having a forward vertical edge, characterized by said bow-bulb projecting Ibeyond the forward vertical edge and below the normal water line of said hull, said bowbulb comprising two lateral faces curved in such a way Vand forming on each side of the hull a longitudinal edge which is Ilocated in the region of the largest transverse width of the bow4bulb, said longitudinal edge sloping rearwardly from said vertical edge in the region behind the forward vertical edge of said hull and having an angle ranging from 6 to 18 relative to `a horizontal plane and extending substantially the entire extent of said bow-bulb, the -portion of the bowabulb behind the rear vertical edge of said forward edge diverging rearwardly relative to a medial plane of said bow-bulb and extending parallel and converging slightly rearwardly not more than 10.

3. The structure as `claimed in claim 2 wherein the longitudinal edge of said bow-bulb is arcuate, the radius of the arcuate edges being less than 0.2\/F wherein F designates the rib surface below the normal water line.

4. The structure as claimed in claim 2 wherein several longitudinal edges are provided on said bow-bulb.

References Cited by the Examiner UNITED STATES PATENTS 551,843 12/1895 Wycherley et al. 114-56 2,191,904 2/1940 Baker 114-56 3,180,299 4/1965 Takao Inui 114-56 MILTON BUCHLER, Primary Examiner.

ANDREW H. FARRELL, Examiner. 

1. IN A SHIP HULL COMPRISING A VERTICAL EDGE AT THE FORWARD PORTION OF THE BOW, A BASE AND A NORMAL WATER LINE, THE IMPROVEMENT COMPRISING A BOW-BULB PROJECTING BEYOND SAID HULL VERTICAL EDGE AND DISPOSED BELOW THE NORMAL WATER LINE, SAID BOW-BULB INCLUDING LATERAL FACES FORMING A LONGITUDINAL EDGE EXTENDING SUBSTANTIALLY FROM THE FORWARDMOST PORTION OF SAID BOW-BULB AND REARWARDLY AND ANGULARLY TOWARD THE BASE OF SAID HULL, SAID LONGITUDINAL EDGE BEING DISPOSED AT THE MAXIMUM TRANSVERSE WIDTH OF SAID BOW-BULB AND EXTENDING SUBSTANTIALLY THE ENTIRE LENGTH OF SAID BOW BULB. 